We present a comparison between the ionized gas and stellar kinematics for a sample of five early-to-intermediate disc galaxies.
We measured the major axis V and σ radial profiles for both gas and stars, and the h3 and h4 radial profiles of the stars. We also derived from the R-band surface photometry of each galaxy the light contribution of their bulges and discs. In order to investigate the differences
between the velocity fields of the sample galaxies we adopted the self-consistent dynamical model by Pignatelli and Galletta
(1999), which takes into account the asymmetric drift effects, the projection effects along the line of sight and the non-Gaussian
shape of the line profiles due to the presence of different components with distinct dynamical behaviour. We find for the
stellar component a sizeable asymmetric drift effect in the inner regions of all the sample galaxies, as results from comparing
their stellar rotation curves with the circular velocity predicted by the models. The galaxy sample is not wide enough to
draw general conclusions. However, we have found a possible correlation between the presence of slowly rising gas rotation
curves and the ratio of the bulge/disc half-luminosity radii, while there is no obvious correlation with the key parameter
represented by the morphological classification, namely the bulge/disc luminosity ratio. Systems with a diffuse, dynamically
hot component (bulge or lens) with a scale length comparable to that of the disc are characterized by slowly rising gas rotation
curves. On the other hand, in systems with a small bulge the gas follows almost circular motions, regardless of the luminosity
of the bulge itself. We noticed a similar behaviour also in the gas and stellar kinematics of the two early-type spiral galaxies
modelled by Corsini et al.(1998).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
The spiral galaxy NGC 3521 exhibits apparently normal kinematic properties of gas and stars along its major axis. However,
the analysis of the LOSVD reveals strong asymmetries. A decomposition of the LOSVD data with a two-Gaussian component model
shows two counter-rotating stellar components. The observed kinematic decoupling is interpreted as a projection effect induced
by the presence of a bar component seen almost end on. The bar produces locally a greater concentration of retrograde stellar
orbits but this does not relate to a specific counter-rotating population. The signatures of the bar are identified in the
velocity field derived from long-slit spectra obtained along the major, minor and 45° intermediate axes and from R-band surface photometry.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
The R-band isophotal map of the Sa galaxy NGC 4698 shows that the inner region of the bulge is elongated perpendicularly to the
major axis of the disc. At the same time a central stellar velocity gradient is found along the minor axis of the disc. The
same properties have also been recognized in the Sa galaxy NGC 4672. This remarkable geometric and kinematic decoupling is
a direct indication that a second event occurred in the history of these galaxies suggesting that acquisition phenomena could
play a primary role in the formation of early-type spirals.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
Landslides are natural hazards that represent a huge economic burden and cause the loss of human life around the world. In countries such as Colombia, the mass movement events that cause the highest number of deaths and economic losses are often related to river or stream flooding caused by landslides in basins. Therefore, it is necessary to develop tools that estimate and assess landslide risk in such areas. This study presents a methodology to assess the risk associated with landslides in streams or river basins. The hazard posed by landslides is evaluated considering probabilistic methods that include the effects of rainfall and earthquakes. In addition, this study assesses the probability of a sliding mass reaching riverbeds and the probability of riverbed obstruction. Vulnerability is then estimated using impact curves based on the obstruction height. Finally, risk is estimated as the probability that economic losses occur along the riverbed. This methodology is based on probability methods, such as the first-order second-moment (FOSM) method, and the punctual estimates method (PEM). The methodology was applied in the La Liboriana River basin, in the municipality of Salgar in the northwestern Colombian Andes. On May 18, 2015, this mountainous and tropical area suffered a flash flood caused by landslides in the basin, which killed more than 100 inhabitants and caused infrastructure damage and significant economic losses. The results suggest that the proposed method coherently assesses the hazard posed by landslides and that the expected losses are comparable with the records from previous events.
In a former paper, we have presented spectra of 64 active, nine normal and five starburst galaxies in the region around the near-infrared calcium triplet (CaT) absorption lines and the [S iii ]λ9069 line. In the present paper, we analyse the CaT strength ( W CaT) and kinematical products derived in that study, namely stellar (σ★) and ionized gas (σgas) velocity dispersions. Our main results may be summarized as follows. (1) Type 2 Seyfert galaxies show no sign of dilution in W CaT with respect to the values spanned by normal galaxies, even when optical absorption lines such as the Ca ii K band at 3933 Å are much weaker than in old, bulge-like stellar populations. (2) The location of type 2 Seyfert galaxies in the W CaT– W CaK plane is consistent with evolutionary synthesis models. The implication is that the source responsible for the dilution of optical lines in these active galactic nuclei (AGN) is a young stellar population, rather than an AGN featureless continuum, confirming the conclusion of the pioneer study of Terlevich, Díaz & Terlevich. (3) In type 1 Seyfert galaxies, both W [S iii ] and W CaT tend to be diluted due to the presence of a non-stellar component, in agreement with the unification paradigm. (4) A comparison of σ★ with σgas (obtained from the core of the [S iii ] emitting line) confirms the existence of a correlation between the typical velocities of stars and clouds of the narrow line region. The strength and scatter around this correlation are similar to those previously obtained from the [O iii ]λ5007 linewidth. 相似文献
An extensive Posidonia oceanica meadow was partially destroyed by excavation, resulting in areas of seagrass habitat of equal complexity (shoot density) but different heterogeneity (degree of fragmentation). The fish assemblages associated with differently fragmented beds were compared from a landscape perspective. Differences in the fish assemblages were detected, with several species showing different patterns: (1) species that increased their abundance along with the degree of bed fragmentation, (2) species that were more abundant in fragmented beds, but did not show differences between more or less fragmented beds, and (3) species that were mostly abundant in large seagrass patches or in the continuous meadow. The fish assemblages were also affected by depth, but further research is needed to determine properly this effect. Some ecological mechanisms are suggested to operate in the interaction between P. oceanica and the held fish assemblage. 相似文献
DDT, DDE and some additional lipophilic derivatives are recognized contaminants in sediments of Southern California Bight (SCB). Only about 10% of total DDTs discharged into the SCB are accounted for using available monitoring data (sediment, water, and biota). DDA represented up to 0.03% DDTs (DDT/DDE/DDD) in SCB surface sediments (top 2 cm) in amounts up to 76 μg DDA/kg dry weight. Highest DDA levels were found where DDT and DDD levels were maximal at the primary wastewater outfall indicating a natural precursor-product relationship for DDT and DDA. Still culture of SCB sediment revealed limited DDA formation following DDT fortification. DDA residues have also been found in contaminated Long Island, NY sediments provided by USGS. The formation of DDA and its potential release from sediments may be significant in resolution of uncertainties concerning the natural recovery of sediments in DDT-contaminated environments. 相似文献